A pyrogenic oxide is an oxide powder material prepared from the hydrolysis-polycondensation of halide such as silicon tetrachloride, methyl trichlorosilane, titanium tetrachloride and aluminium chloride, used as a raw material at high temperatures. The principle of the hydrolysis-polycondensation is as follows:MClx+H2+O2→M2OxHCl.
It can be known from the above reaction equation that a hydrogen chloride gas is generated during the course of reaction. This gas makes the oxide powder material have strong acidity by adsorbing at its surface and affects its application. Thus it generally needs to remove the acid gas absorbed at the surface of the oxide powder material by deacidifying during the production.
The existing deacidification technology uses a high temperature desorption with assisted deacidification medium way for deacidification, i.e., the acid gas adsorbing at the surface of the oxide powder material can be desorbed at high temperatures by burning, electrical heating or infra-red heating to achieve deacidification. The deacidification apparatus to be used is a vertical or horizontal deacidification furnace which uses internal heating, jacket heating, infra-red heating or the like. As ZL 02149782.6 or ZL 200410051507.6, arranging heating tubes in the deacidification furnace in a crossover manner, heating to 450˜750° C., and supported by a deacidification medium such as hot air, water vapor or the like, for deacidification, the desorbed is discharged together with the deacidification medium. The traditional technology has defects which cannot be overcome by itself. Firstly, the deacidification requires a high temperature that the temperature should remain in 400˜750° C. inside the furnace, which leads to great energy consumption during deacidification. Secondly, the powder material is easy to be discharged with the deacidification medium, so it needs to provide a filter such as bag-type dust remover in the exhaust outlet of the deacidification furnace, but the filter is likely to bring blocking, which causes the pressure of the system to destabilize. Further, the deacidification in traditional technology is inefficient, in order to assure that the acid gas adsorbing at the surface of the powder material can be effectively removed, the height (length) of the deacidification furnace is relatively large to ensure the powder material can stay in the furnace long enough, and sometimes even the second or third deacidification is needed to ensure the PH value of the suspension 4 wt % aqueous solution of the deacidified product is larger than 3.6.
ZL 200810058544.8 uses an infra-red heating way for deacidification. The principle of infra-red heating is that the water and HCL molecules in the powder rotate quickly and rub against each other to generate heat to heat the powder with the action of a microwave alternating electromagnetic field, which requires high water content in the powder that is regularly more than 10%. For a powder material prepared from pyrolysis, the water content is at a low level during production of the powder material, and the powder material forms a branch structure of spherical particles held together loosely, such that the loose structure tends to be collapsed after it is processed at high temperature in high water content, resulted in the collapse of the structure that it is easy to lose the specific features of the superfine powder from pyrolysis such as thickening, thixotropy, extinction and so on. Moreover, the processing efficiency of the microwave heating per apparatus time is relatively low, so it is not good for mass powder deacidification.